Production of aromatic hydrocarbons of high purity



May 25, 1948.y n, M. SHEPARDsoN PRODUCTION OF AROIATIC HYDROCARBONS 0F HIGH PURITY Filed Hay 6, 1943 2 SheetsPSheet 1 NJOQU NIUNK May 25, 1948. R. M. sHEPARDsoN CTION 0F ROMATIC HYDROCARBONS OF HIGH PURITY PRODU Filed may e, 194:5

2 Sheets-Sheet 2 Patented May 25, 194s PRODUCTION OF AROMATIC HYDRO- CARBONS OF HIGH PURITY Robert M. Shepardson, Madison, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application May 6, 1943, Serial No. 485,797

4 Claims. (Cl. 26o-673.5)

This invention relates to high temperature cracking of hydrocarbons under relatively low pressure to produce aromatic constituents.

Steam cracking of hydrocarbon oils or liquid fractions is known for the production of oleflns, diolens, and aromatic compounds. The desired aromatic compounds comprise benzene and toluene but in the ordinary steam cracking operations they are contaminated by undesired parailns and olens having substantially the same boiling point and it is impossible, for example, to separate nitration grade toluene from such mixtures by distillation.

Other processes are known in which mixtures of aromatics and parailins are obtained and the desired aromatics are separated by solvent extraction from the parain compounds.

According to my invention, normally liquid hydrocarbons are severely cracked at relatively high temperatures for a relatively short period of time in the presence or absence of a diluent gas to substantially completely destroy all parafiins and olens in the boiling range of benzene and higher boiling aromatics.V sible to crack hydrocarbons, fractionally distill the cracked mixture toseparate a toluene fraction and a benzene fraction, acid treat the fractions separately and again distill each fraction With my invention it is posto obtain nitration grade of toluene and subi stantially pure benzene without the necessity of solvent extracting.

In the drawings, Figs, 1 and 1A represent one form of apparatus adapted to carry out my invention, Fig. 1A being a continuation of Fig. 1.

Referring now to the drawings, the reference character i0 designates a line through which the charge stock or feed stock is pumped by pump l2. The charge stocks which may be used in my invention may be any petroleum fraction although heavy naphthas with a boiling point of about 200 F. to 300 F. to about 200 F. to 400 F. are preferred. Virgin fractions from parafnic or naphthenic type crudes or cracked fractions of more olenic structure may be used. Diluent gas such -as steam, light normally gaseous hydrocarbons, flue gas or other inert gas is introduced into line I0 through line I4. While I prefer to use a diluent, my process may be carried out without using any diluent gas. Instead of using an inert diluent gas, I may use air or other oxy= gen-containing gas which will aid ln raising the temperature of the mixture by burning some of the hydrocarbons and will also lead to the production of liuc gas by the resulting combustion.

The charge stock with or without an added diluent gas is passed through a heating coil I6 in reaction zone I8 where the temperature is rapidly raised to about 1200 F. to about 1600 F. The time of reaction is maintained from about a few seconds to a fraction of a`second depending on the temperatures used. The temperature during reaction is suiliciently high to destroy substantially all of the paraffin compounds boiling in the desired aromatic range and at the same time olens, dioleflns and desired aromatic cornpounds are produced.

The cracked mixtureleaving the reaction Zone I8 is immediately quenched to a, temperature of about 600 F, to 1000 F. by the introduction of water through line 22. l The quenched mixture passes through line 24 into the lower portion of a cooling tower 26 where additional water quench is introduced at the top of the cooling tower through line 28. i

In the cooling tower 26 the reaction products are cooled to below the boiling point of water so that water and some of the normally liquid hydrocarbons are condensed and are collected in the bottom of the cooling'tower. The water forms the lower layer 32 and this water is withdrawn from the bottom of the tower 26 and passed through line 34 and cooler 36. At least a portion of the cooled water is passed through line 38 by pump 42 and returned to the quench lines 22 and 28. If steam is used as avdilu'ent, at least a portion of the Water is withdrawn from line 34 through line 44 and removed from the system.

The condensed oil or normally liquid hydrocarbons form the upper layer 46 in the bottom portion of the cooling tower 26 and the liquid hydrocarbons are withdrawn from the tower and passed through line 48 by pump 52. The liquid oil contains olens, dioleflns and the desired aromatic fraction as well as heavier aromatic constituents. The oil is then passed through line 54 and heating coil 56 in a heater 58 and then passed into fractionating tower 62 for separating the oil into the desired fractions as will be presently described.

In the cooling tower 26 normally gaseous constituents and some higher boiling constituents are not condensed and pass overhead through line 64 to a compressor 66 where they are compressed to a pressure of about to 600 lbs/sq. in. and the compressed gases are introduced into an absorber 68. Cool absorber oil is introduced into the vtop of the absorber or absorption tower through line 'l2 for countercurrent scrubbing of the gases introduced through line 64. During this scrubbing, desired constituents are recovered from the gas and the gases which are not absorbed pass overhead through line 14 and are vented from the system. Desirable constituents are absorbed in the absorber oil. If it is desired to recover the ethylene, high pressure absorption would be employed, whereas low pressure absorption is satisfactory if only the C4 and higher boiling fractions are wanted;

The fat absorption oil is withdrawn from the bottom of the absorber 68 through line 16 and is passed through a heating coil 18 in a heater 82 to remove the absorbed constituents from the absorber oil yand the heated mixture is then passed to a stripping zone or stripper tower 84 wherein the vaporized constituents are separated from lean absorption oil which is withdrawn from the bottom of the stripper tower 84 through line 86 and pumped through this line by a pump 88. The lean absorber oil is then passed through a cooler 92 and the cooled absorption oil is then returned and into the fractionating tower 62 above described.

In the fractionating tower 62 the mixture is fractionated to separate the cracked products into desired fractions. The fraction going overhead through line 96 may comprise a C2 through Csfraction containing ethylene, propillene, isobutylene, n-butylene, butadiene, pentylene, and the various C5 diolefins. This gaseous fraction can be further treated in any of-the various well known methods to separate any of the desired oleiins or dioleiins from the remaining constituents. From the upper portion of the fractionating tower 62 another fraction is removed through line 98 and. this fraction comprises Cs paraiiins and oleiins.

Further down in the tower another fraction is taken oi through line |02 and this fraction is a benzene cut containing a large percentage of benzene and a small quantity of olefins and dioleiins. Further down in the tower another aromatic fraction is taken oi through line |04 and this fraction contains a large proportion of toluene and a small quantityof olei'l-.ns and dioleiins.

Further down in the fractionating tower a heavy naphtha fraction is removed through line |06 and this heavy fraction is removed from the system. The heavy naphtha fraction may be recycled to the heating coil I6 or it may be removed from the system and further treated to produce motor fuel, aviation blending stock, etc. The heavy naphtha. fraction is highly aromatic and forms a good motor fuel. By clay treating this heavy naphtha an aromatic-motor fuel is obtained. Bottoms comprising tar or fuel oil are withdrawn from the bottom of the fractionating tower through line |08.

The further treatment of the toluene fraction will now be described. This toluene fraction comprises about 97% toluene and some olefns and dioleiins and practically no parafiin compounds. The toluene fraction is passed through line |04 by pump ||2 and is mixed with an acid such as concentrated sulfuric acid introduced through line |I4 to remove oleiins and dioleiins from the toluene fraction. Preferably a countercurrent system is used with cooling between the stages to reduce sulfonation of the aromatic constituents.

The concentration of the acid is preferably from to 98% and the guantity of acid used or needed will vary depending on the quantity of olefns and -diolens present, about 25 lbs. of sulfuric acid per barrel of toluene fraction generally being suilicient.

The mixture of acid and toluene fraction is'introduced into a mixing zone I6 for intimate mixture of the acid and toluene fraction and the mixture is then passed through line ||8 to a separator 9. The acid used for mixing with the toluene fraction is acid recovered from a. latter separating stage as will be presently described. In the separator ||9 acid sludge containing olefins and dioleiins settles in the bottom of the settling chamber ||9 and is removed from the system through line |22. Y

The partially treated toluene fraction is then passed overhead through line |24 and through a cooler |26 after which it is mixed with an additional quantity of acid introduced through line |21. This acid is taken from the third separating stage as will be presently described. The mixture of acid and toluene fraction is introduced into a second mixer |28 where further intimate contact between the acid and toluene fraction is brought about. 'I'he mixture is then passed through line |34 to a second separating or settling chamber |36 in which the acid separates as a lower layer and is withdrawn from the bottom of the settling chamber through line |I4 and pumped through this layer by pump |38. Line ||4 introduces the partly used acid into line |04 for admixture with the untreated toluene fraction from the fractionating tower 62 before being passed to the first mixer H6,

The further treated toluene fraction leaves the settling chamber |36 through line |44 and is passed through a. cooler |46. Fresh sulfuric acid is introduced into line |44 by line |48 and this mixture is introduced into a third mixing zone |52 where the purified toluene fraction is contacted with fresh acid to further remove undesirable constituents. The mixture is then passed through line |54 to a third settling chamber |56 in which the acid settles as a lower layer and is withdrawn from the bottom of the settling chamber through line |21. The acid is passed through line |21 by pump |62 and is introduced into line |24 as above described for admixture with the partly purified toluene fraction passing to the second mixer |28.

The purified toluene fraction leaves the settling chamber |56 through line |64 and is passed through heating coil |66 in heating zone |68 and then through line |12 into a second fractionating tower |14. In the fractionating tower |14 the toluene fraction is further fractionated and nitration grade toluene meeting the U. S. Army specification is withdrawn through line |16. Bottoms from the fractionating tower |14 are withdrawn through line |18 and overhead gases or vapors from the fractionating tower |14 are passed through line |82. The bottoms and the overhead gases or vapors are combined and passed through line |84 by pump |86 and admixed with the oil or cracked products leaving the cooling tower 26 and this mixture is introduced into the first-fractionating tower 62 for the recovery of benzene and toluene which does not quite meet desired purity.

The further treatment of the benzene fraction withdrawn through line |02 will now be described. This'benzene fraction is treated in a similar manner to the treatment for the toluene mixed with fresh sulfuric acid fraction. The benzene fraction is pumped through line |02 by pump 202 and is mixed with partly used acid from a second settling chamber, the acid being passed through line 204 and introduced into the benzene fraction in line |02. The mixture is passed through a first mixer 206 and the mixture is then passed through line 208 to a rst settling chamber 2|2 in which the acid settles as a sludge containing oleiins and dioleiins and is withdrawn through the bottom of the settling chamber through line 2I4 and removed from the process.

The separated benzene fraction in partly purified form is removed from the rst settling chamber 2|2 through line 2|6 and passed through a cooler 2|8 after which it is mixed with partly spent acid from the last settling chamber, the partly spent acid being passed through line 220. This mixture is passed to a second mixing zone 222 and the mixture is passed through line 226 to a second settling chamber 228 in which the acid settles as a bottom layer. This acid is the partly spent acid which is returned through line 204 by pump 234 for admixture with the impure benzene fraction being introduced into the purifying system.

The separated partly purified benzene fraction leaves the settling chamber 228 through line 236 and is passed through cooler 238 after which it is introduced through line 242. This mixture is passed to a third mixing zone 244 and then through line 246 to a third settling chamber 248 in which the partly spent acid separates as a bottom layer. This bottom layer is passed through line 220 by pump 254 and is the acid which is mixed with the partly purified benzene fraction passing through line 2 I6 after the first purifying step.

The puried benzene fraction is withdrawn from the settling chamber 248 through line 256 and is passed through a heating coil 258 in a heating zone 262 to heat the fraction to distillation temperature. The heated fraction is then passed through line 264 and is introduced into the lower portion `of a third fractionating tower 268 for separating benzene of about 99+% purity. The purified benzene is withdrawn through line 212. The, bottoms are withdrawn through line 214 from the fractionating tower 268. Overhead vapors and gases are withdrawn through line 216. The bottoms and overhead vapors and gases are mixed and passed through line 218 for admixture with the overhead vapors and bottoms from the second fractionating tower |14 for return to the first fractionating tower 62. The bottoms and overhead vapors or gases from the third fractionating tower 268 contain impure benzene which is returned to the first fractionating tower |52A for further treatment.

The time of mixing of acid and the benzene or toluene in each mixing zone is about 3 minutes. A settling time in each separating chamber following mixing is about 5 minutes. I am not to be limited exactly tothese times as they may be varied within limits without departing from my invention. The acid treatment is carried out at temperatures so that the benzene and toluene are in liquid phase.

My invention is especially adapted for cracking heavy naphthas to produce exceedingly pure benzene and toluene. In the following example East Texas heavy virgin naphtha having a boiling range of about 250F. to 400 F. was cracked in the presence of steam at about lbs. gauge pressure. The amount of steam used was about 80 mol percent. In the following data the two columns compare the results 4obtained by practicing my invention to produce pure toluene and benzene with an operation for producing maximum butadiene. v

Steam cracking East Texas heavy virgin naphtha of mol per cent steam.

O eration G vin Ni- Oeration trat on iving Grade Tolu- Maximum ene Alter Butadiene c Treating Temperature ..F. 1, 400 1, 375 Feed Rate, v.{lv./hr. to Highest Teml erature Co 2.9 8.9 T mes of Contact seconds.. 0.83 0.27 Yields: C. Free Gas.. wt per cent.. 51.5 39.8 Ethylene. do l5. 3 14. 1 Total C do 5. 65 10.07 Butadiene. do 2. 99 3. 83 Isobutylene. do 1. 67 2. 47 N-butylene- .do.... 0. 74 3. 64 Total 0| do-.-. 2.00 6.03 Isoprene .-do-. 0.37 1.65 Pipe lene .do 0.47 1. 42 Debutanized Gasoline. ol per cent.. 26.0 45. 2 Toluene 0.... 5. 4 3.1 Benzene.v .do 7.6 2.3

readily removed by acid treatment. In the sec-- ond or less severe operation giving maximum butadiene, however, the benzene and toluene fractions contained 40% to 60% of olens and diolefins which past experience has shown cannot besatisfactorily removed by acid treatment without tremendous losses of the desired aromatics.

The cracked products passing to the fractionating tower 62 from the rst or more severe oper` ation above were fractionated in a one hundred plate distillation tower to separate a toluene fraction and a benzene fraction. The separate fractions were then treated with about 25 lbs. of 98% sulfuric acid per barrel of oil passing to the fractionating tower 62.

After the acid treatment, the benzene and toluene fractions were each passed to a separate fractionating tower comprising a 40 plate column in which these puriiied fractions were separately fractionated. The toluene produced satisfactorily met U'. S. Army specication for nitration grade toluene and the benzene was about 99.5% purity.

As above pointed out, the operating temperature range is about 1200 F. to 1600 F. but for the treatment of heavy naphthas a temperature of about1400 F. is preferred.

Data have been obtained indicating the time of contact required at various temperature levels to eiect cracking of the hydrocarbons` of sufficient severity to destroy the parafiins thus permitting the production of pure benzene and toluene without solvent extraction. The empirical formula for this correlation in the temperature range of about 1200 F. to 1600 F. is as follows. The temperature (T) in degrees Fahrenheit must be equal to or greater than 1332-107.6 log S+10S1-45 where S is the actual time of contact in seconds at the temperature T.

Since in most cases the cracking will not be carried out at a constant temperature level, it will be necessary to correct the times of contact at' the various temperature levels to a time of conact at a common temperature level. This canbe accomplished with the aid of th'e empirical formula in which all points obtained are of equal cracking severity. The following equation can' be used to calculate equivalent contact time at any temperature level.

' tern time j; ,y Time at :c tem Ime req at y empTine reqd 1 atx temp. l Time required to destroy paramns in boiling range of aromatica according to my invention. v

For` example, if there is an operation in which the time of contact is 0.2 second at 1300 F., 0.2 second at 1350 F. and 0.2 second at1400 F. and 0.1 second at 1450 F., the equivalent time of contact at 1450 F. in each zone is as follows:

At 135o 5=25 03=0-004 second at 1450 F.

Ac 1400 F--- f o=0120 second at 1450 F.

At 1450o F 0.100 second at 1450 F.

Total 0.311 second at 1450" F.

In the above data the 2.2 'factor is obtained by using the empirical formula to obtain the time required at 1300 F. to obtain the degree of cracking required by my invention. The denominators in the 1350 F. and 1400 F. are similarly obtained for these temperatures. 'I'he 0.3fact0r is obtained from the formula. by solving for the time required at 1450 F. y

The total vabove shown is greater than 0.3 and as this is the equivalent time for cracking at 1450 F., these conditions are suiilciently severe to destroy parainns and come under the operating conditions set forth in my invention.

When employing cracking conditions on normal petroleum hydrocarbons fullling the vrequirements of the above empirical fornula, it has been found that the concentration of paraillns in the fraction boiling from 170 F. to 240 F. from the product is not over 1 volume per cent, with olefin and diolen concentration varying from 2 to 9 volumes per cent and aromatic concentration exceeding 90 volume per cent. Because of the almost complete absence of paraillns and the low concentration of oleiins or diolefins, acid treatment followed by distillation to remove polymers is suicient to produce aromatics of greater than 99% purity. With milder cracking conditions, however, solvent extraction in addition to acid treatment is necessary to obtain aromatics of this purity.

After acid-treating the benzene and toluene cuts, they may be given usual water 'washing treatment followed by usual alkaline washes to remove acidic constituents. l

While I have shown one form of apparatus and have included a specific example, it is to be understood that these are by way of illustration only and my invention is not to be limited thereto.

I claim:

1. A method of producing an aromatic fraction in the gasoline boiling range from relatively heavy naphthas which comprises heating heavy naphtha containing parailin constituents to a temperature of about 1400 F. for a period of time in the range o! about 0.5 of a second to about 1.0 second to substantially completely destroy the paraillnic constituents in the naphtha in the boiling range of the desired aromatic fraction and form aromatic compounds and olens and dioleilns, fractionating in arectii'ying column the cracked products to separate therefrom an aromatic traction in the desired boiling range substantially free of paraillnic compounds and of normally gaseous olens, further treating the aromatic fraction thus separated with concentrated sulfuric acidv to remove olefins and diolediluent gas is mixed with the naphtha before y heating vto 1400 F.

ROBERT M. SHEPARDSON.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,441,341 Govers Jan. 9, 1923 1,483,835 Ramage Feb. 12, 1924 1,679,093 Miller et al. July 31, 1928 1,741,305 Jaeger Dec. 31, 1929 1,847,239 Frey et al. Mar. 1, 1932 2,052,852 Stark et al. Sept. 1, 1936 2,057,007 Cambron et al. Oct. 13, 1936 2,113,536 Grebe et al. Apr. 5, 1938 2,133,344 Cooke Oct. 18, 1938 2,147,399 Borden Feb. 14, 1939 2,222,128 Wagner Nov. 19, 1940 2,232,761 Balthis Feb. 25, 1941 2,263,557 Greenewalt Nov. 25, 1941 2,340,815 Lidov Feb. l, 1944 2,345,600 Heard et al. Apr. 4, 1944 2,346,642 Babcock et al. Apr. 18, 1944 2,349,045 Layng et al May 16, 1944 FOREIGN PATENTS Number Country Date 107,669 Australia June 22, 1939 115,066 Great Britain Apr. 22, 1918 OTHER REFERENCES Lisle, Ref. and Nat. Gasoline M fr. 20 No. 8, pages 294-300, Aug. 1941.

Dobryanskii et al., Trans. of Research Plant Khimgaz. Materials on Cracking and Chemical Treatment of Cracked Products. 2 60-97 (1935). 0. N. T. I., Leningrad. Translation available, s-184 of Survey of Foreign Petroleum Literature, pages 1-27, in 260-680. Page 34 of the translation contains a bibliography of 3 references. 

